1. Field of the Invention
This invention relates to a method for providing control of high power laser-fiber delivered beam quality. Such structures of this type, generally, use a fiber output end preparation to improve the beam quality of fiber delivered laser beams.
2. Description of the Related Art
Laser materials processing as known in the art and as used herein refers to performance of materials processes, such as cutting, welding, drilling and soldering, with a high a power continuous wave or pulsed laser beam. The average power of a high power laser beam may range from as little as approximately 1 watt to hundreds of watts. A user selects the specific power of the beam on the basis of a particular process being performed.
Known art describes transmitting a laser beam from a laser source to the vicinity of a workpiece by means of an optical fiber. For example, an apparatus and method for injecting a power laser beam into an optical fiber for transmission therethrough are described in commonly assigned U.S. Pat. Nos. 4,564,736, 4,676,586, and 4,681,396, respectively entitled "Industrial Hand Held Laser Tool and Laser System", "Apparatus and Method for Performing Laser Material Processing Through a Fiber Optic", and "High Power Laser Energy Delivery System", the disclosure of each of these patents being incorporated in their entirety herein by reference.
Transmitting a laser beam through an optical fiber to an output coupler also is known. Such an apparatus is described in commonly assigned U.S. Pat. No. 4,799,755, entitled "Laser Materials Processing with a Lensless Fiber Optic Output Coupler", the disclosure of which is incorporated in its entirety herein by reference. In the apparatus described in U.S. Pat. No. 4,799,755, lens systems are not utilized in an output coupler. Rather, a fiber injecting lens is selected to have a focal length of sufficient length to enable the use, for materials processing, of the diverging beam emitted at an output end of the fiber without a need for a beam focusing lens-type output coupler.
An output coupler having a lens system therein for focusing a laser beam transmitted thereto through an optical fiber is disclosed in commonly assigned U.S. Pat. No. 4,844,574, entitled "Optical Fiber Output Coupler for a Power Laser", the disclosure of which is incorporated in its entirety herein by reference. The apparatus described in U.S. Pat. No. 4,844,574 includes a lens system that compensates for adverse effects of fiber transmission in order to improve focused spot power density of the fiber transmitted beam.
Still other known laser material processing systems utilize lens systems at an output of a laser source. Such systems are described in commonly assigned U.S. Pat. Nos. 3,419,321 and 4,275,288, entitled "Laser Optical Apparatus for Cutting Holes" and "Apparatus for Machining Material", respectively. In each of these systems, optical fibers are not utilized. Therefore, since a laser source generally is a stationary system, at least during a materials processing operation, lenses are aligned with the beam directly output by the laser source. The mobility of such systems is limited, therefore, the need for high power fiber optic beam delivery. If this laser beam is not properly delivered to the output coupler from the fiber output, the quality of the beam emitted from the output coupler will be adversely affected.
The beam quality out of an optical fiber has been shown to improve by injecting the optical fiber with long focal length lenses. Long lens injection into the fiber reduces the exiting beam divergence out of the fiber. Exemplary of such long
is U.S. patent application Ser. No. 07/950,567, now U.S. Pat. No. 5,245,682, to A. L. Ortiz, Jr. entitled "Fiber Optic Delivered Beam Quality Control System for Power Lasers". The other method of improving the fiber delivered beam quality is by reducing the fiber core diameter. The use of small core diameter fibers require high beam core lasers such as a face pumped laser (FPL). The combination of fiber core diameter and long focal length injection can be optimized but there are definite limits. One such limit is the laser beam is spot sized which must be smaller than fiber diameter and cannot exceed the fiber numerical aperture (NA). Therefore, a more advantageous system, then, would be presented if the fiber optic delivered beam quality could be improved.
It is apparent from the above that there exists a need in the art for a fiber optic end preparation for improving fiber delivered beam quality for power lasers which is capable of adequately delivering the beam to the output coupler, and which at least equals the delivered characteristics of the known high power laser energy delivery systems, but which at the same time substantially increases the quality of the fiber optic delivered beam. It is a purpose of this invention to fulfill this and other needs in the art in a manner more apparent to the skilled artisan once given the following disclosure.